DE602005003805T2 - EXHAUST GAS CLEANING DEVICE AND EXHAUST GAS CLEANING PROCEDURE FOR INTERNAL COMBUSTION ENGINE - Google Patents

Description

Technical part

The The present invention relates to an exhaust gas purification apparatus and a Emission control method for an internal combustion engine.

Technical background

A typical exhaust gas purifier applied to an internal combustion engine such as a vehicle diesel engine has a particulate filter (refer to FIG Japanese Patent Laid-Open Publication No. 2002-227688 ), which is located in an exhaust system. The particulate filter detects particulate matter ("PM") composed mainly of soot or unburned carbon in an exhaust gas In an internal combustion engine provided with an exhaust gas purifying apparatus, a solids removal control is performed to prevent the particulate matter filter from being added with particulates In solids removal control, solids are burned and removed.

In the solids removal control, which in a Japanese Patent Laid-Open Publication No. 2002-227688 is disclosed, the exhaust air-fuel ratio is reversed between a rich state and a lean state to supply an unburned fuel component and oxygen to a catalyst of the particulate filter. Oxidation of the unburned fuel component is used to increase the catalyst bed temperature and to burn solids in the particulate filter. The supply of an unburned fuel component to the catalyst in the solids removal control is performed in a manner that permits a temperature increase in the catalyst with a minimized amount of unburned fuel. This minimizes extra fuel consumption due to the solids removal control.

however was confirmed, that in the previous solids removal control, not all solids, at the front end of the solids filter (upstream end relative to the flow direction the exhaust gas) are deposited, can be burned. The reasons will be as follows.

The Front end of a solid filter is susceptible to deposition of solids, and the amount of deposited solids is greater than that in the downstream section.

The Solids removal control in which an unburned fuel component and oxygen are supplied to the particulate filter, can not be sufficient Amount per unit time of an unburned fuel component and oxygen, around all solids deposited at the front end of the solids filter to burn.

Corresponding is concluded even if the solids removal control over a extended period accomplished will that unburned PM or solids at the front end of the solids filter remain. If the exhaust gas air-fuel ratio is richer is made after the solids removal control with remaining Solids is terminated, becomes an unburned fuel component supplied to the fuel filter, and oxidation of the unburned fuel causes the To burn solids, which is the catalyst bed temperature of the May excessively increase solids filter.

The device and method used in WO 00/28196 A For example, for heat exchange between the inlet and outlet, exhaust streams provide to enhance the catalyst reactions by placing the catalysts in the temperature zones in which their operations are enhanced to strengthen the catalyst reactions, and also provide for regeneration of a filter that is used to Detecting solids in the streams is used.

Summary of the invention

Corresponding It is an object of the present invention to provide an exhaust gas purifying apparatus for an internal combustion engine to ensure the complete burning of solids in one Solid filter is capable of suppressing deterioration of one Fuel economy or fuel economy, by burning the solids probably caused. The present invention sees Further, an exhaust gas purification method for an internal combustion engine before.

In order to achieve the foregoing and other objects and in accordance with the purpose of the present invention, the invention provides an exhaust gas purifying apparatus for an internal combustion engine. The apparatus performs a solids removal control in which an unburned fuel component is supplied to a catalyst located in an exhaust system of the internal combustion engine so that the temperature of the catalyst is increased and solids stuck to the catalyst are burned. The apparatus includes an executing means, wherein when an accumulation amount of particulates on the catalyst becomes smaller than a first determination value after the solids removal control is started, the executing means executes a burn off control in which execution is performed and stopping a concentrated, intermittent fuel addition to a portion of the exhaust system that is upstream of the catalyst, at a predetermined frequency. A stopper stops the solids removal control based on an end of the burn-off control. A forced completion means forcibly terminates the burn-off control when, after the start of the burn-off control, an elapsed time since the accumulation amount of particulates on the catalyst has fallen to a second determination value reaches a predetermined time. The second determination value is smaller than the first determination value.

Further The present invention provides an exhaust gas purification method for an internal combustion engine in front. The method includes performing a solids removal control in which an unburned fuel component is supplied to a catalyst, which is located in an exhaust system of the internal combustion engine, so that the temperature of the catalyst is increased and solids, the stuck to the catalyst, burned. A burn-off control is running, when an accumulation amount of solids on the catalyst becomes smaller becomes a first determination value after the solid removal control started. In the burn-off control, a performing and stopping a concentrated, intermittent fuel addition to a portion of the exhaust system upstream of the catalyst is repeated at a predetermined frequency. The solids removal control is stopped based on an end of the burn-off control. The burn-off control is forcibly terminated when after the start of the burn-off control an elapsed time, since the accumulation amount of solids was reduced to a second determination value on the catalyst, reaches a predetermined time. The second determination value is less than the first determination value.

Other Aspects and advantages of the invention will become apparent from the following description seen in conjunction with the attached drawings by way of example represents the principles of the invention.

Brief description of the drawings

The Invention, along with tasks and benefits thereof, may be best by reference to the following description of the currently preferred embodiments together with the attached drawings be understood, in which:

1 Fig. 12 is a schematic view showing the overall configuration of an internal combustion engine to which an exhaust gas purifying apparatus according to the present invention is applied;

2 (a) and 2 B) Timing diagrams showing the manner of adding fuel and changes in exhaust gas air-fuel ratio due to fuel addition during burn-off control;

3 Fig. 10 is a flowchart showing an execution of a procedure for the final-stage burn-off control for a solids removal control; and

4 (a) to 4 (d) Timings are the changes in the solid accumulation amount related to the solids removal control and the burn-off control, the state of the solids removal control, the state of the burn-off control and changes of a counter C.

Best ways to run the invention

An exhaust gas purifying apparatus for an internal combustion engine according to a preferred embodiment of the present invention will now be described with reference to FIG 1 to 4 (d) to be discribed.

1 represents the configuration of an internal combustion engine 10 to which an exhaust gas purifying apparatus according to this embodiment is applied. The internal combustion engine 10 is a diesel engine that uses a common rail fuel injector and a turbocharger 11 Has. The machine 10 has a suction passage 12 , Combustion chambers 13 and an outlet passage 14 ,

The inlet passage 12 forms an intake system for the internal combustion engine 10 , In the most upstream portion of the inlet passage 12 there is an air filter 15 , From the air filter 15 towards the downstream side are an air flow meter 16 , a compressor 17 in the turbocharger 11 is installed, an intercooler or intercooler 18 and an intake throttle valve 19 in the inlet passage 12 intended. The inlet passage 12 is at an intake manifold 20 branched downstream of the intake throttle valve 19 located, and with each of the combustion chambers 13 the internal combustion engine 10 through inlet connections 21 connected is.

In the outlet passage 14 , which forms part of the exhaust system for the internal combustion engine, is an exhaust port 22 with each combustion chamber 13 connected. The outlet connections 22 are connected to an exhaust gas turbine 24 of the turbocharger 11 through an exhaust manifold 23 connected. In a section of the exhaust passage 14 which is downstream of the exhaust gas turbine 24 is a NOx catalyst 25 , a solid filter 26 and an oxidation catalyst 27 in that order from the provided upstream side.

The NOx catalyst 25 carries an occlusion reduction NOx catalyst. The NOx catalyst absorbs NOx in exhaust gas when the concentration of oxygen in an exhaust gas is high, and emits the absorbed NOx when the concentration of oxygen in the exhaust gas is low. When a sufficient amount of unburned fuel component functioning as a reducing agent is present in the vicinity of the NOx catalyst, the NOx catalyst reduces NOx emitted to purify the exhaust gas.

The solid filter 26 is made of a porous material and captures particulate matter (PM), which in exhaust gas is mainly composed of soot. Like the NOx catalyst 25 carries the solids filter 26 an occlusion reduction NOx catalyst. The NOx catalyst of the solids filter 26 reduces emitted NOx to purify the exhaust gas. The reaction triggered by the NOx catalyst burns (oxidizes) and removes the stuck solids.

The oxidation catalyst 27 carries an oxidation catalyst. The oxidation catalyst oxidizes hydrocarbon (HC) and carbon monoxide (CO) in exhaust gas to purify the exhaust gas.

In sections upstream and downstream of the solids filter 26 are each an input gas temperature sensor 28 and an exit gas temperature sensor 29 intended. The inlet gas temperature sensor 28 detects an input gas temperature, which is the temperature of exhaust gas that enters the solids filter 26 flows. The outlet gas temperature sensor 29 detects an exit gas temperature, which is the temperature of exhaust gas passing through the solids filter 26 has passed through. Also a differential pressure sensor 30 is in the exhaust passage 14 intended. The differential pressure sensor 30 detects a pressure difference between an upstream portion and a downstream portion of the particulate filter 26 , oxygen sensors 31 . 32 are each located in a section of the exhaust passage 14 upstream of the NOx catalyst 25 is, and a portion of the exhaust passage 14 between the solid filter 26 and the oxidation catalyst 27 , The oxygen sensors 31 . 32 detect the oxygen concentration in the exhaust gas.

The internal combustion engine 10 further comprises an exhaust gas recirculation device (EGR device) for returning a part of the exhaust gas to the air in the intake passage 12 on. The EGR device has an EGR passage 33 on, the exhaust passage 14 with the inlet passage 12 combines. The furthest upstream section of the EGR passage 33 is with a section of the exhaust passage 14 connected upstream of the exhaust gas turbine 24 lies.

In the EGR passage 33 are an EGR catalyst 34 , an EGR cooler 35 and an EGR valve 36 provided in this order from the upstream side. The EGR catalyst reforms recirculated exhaust gas. The EGR cooler 35 cools the reformed or improved exhaust gas. The EGR valve 36 adjusts the flow rate of the improved and cooled exhaust gas. The most downstream section of the EGR passage 33 is with a portion of the intake passage 12 connected downstream of the intake throttle valve 19 is.

An injection device 40 is in every combustion chamber 13 the internal combustion engine 10 provided to burn fuel into the combustion chamber 13 inject. Injectors 40 are with a common rail 42 with a high pressure fuel line 41 connected. High pressure fuel is through a fuel pump 43 to the common rail 42 fed. The pressure of the high-pressure fuel in the common rail 42 is through a line pressure sensor 44 detected, to the common rail 42 is attached. The fuel pump 43 is for supplying low pressure fuel through a low pressure fuel line 45 to a fuel addition valve 46 in a position.

Various control procedures for the internal combustion engine 10 are from an electronic control device 50 executed. The electronic control device 50 has a CPU, the various calculation processes related to a control of the machine 10 executing a ROM which stores programs and data required for the control, a RAM for temporarily storing the calculation results of the CPU, and input and output terminals for inputting and outputting signals to and from the outside.

In addition to the sensors described above, the input terminal of the electronic control device 50 with a NE sensor 51 for detecting the speed of the machine 10 , an accelerator pedal sensor 52 for detecting the degree of depression of the accelerator pedal and a throttle valve sensor 53 for detecting the opening degree of the intake throttle valve 19 connected. The output terminal of the electronic control device 50 is with a drive circuit for driving the intake throttle valve 19 , the EGR valve 36 , the injector 40 , the fuel pump 43 and the fuel addition valve 46 connected.

Based on detected signals from the The sensors described above detect the electronic control device 50 the operating condition of the machine 10 , According to the detected operating state, the electronic control device outputs 50 Control signals to the drive circuits of the devices which are connected to the output terminal. The electronic control device 50 executes various control procedures, such as control of the opening degree of the intake throttle valve 19 , an EGR control based on the opening degree control of the EGR valve 36 , a control of the amount, times and pressure of a fuel injection from the injector 40 and control related to fuel addition by the fuel addition valve 46 ,

In this embodiment, the NOx catalyst 25 and the solid filter 26 to stop being clogged with solids, the solids removal control is carried out by the NOx catalyst 25 and the solid filter 26 captured solids are burned to purify an exhaust gas. In the solids removal control, an unburned fuel component becomes the NOx catalyst 25 and the NOx catalyst of the particulate filter 26 supplied so that the unburned fuel component in the exhaust gas or at each catalyst is oxidized to generate heat. Accordingly, the catalyst is heated to a temperature of about 600 to 700 ° C and solids on the catalyst are burned.

During the solids removal control, an unburned fuel component may be supplied through an auxiliary injection (after injection) into an exhaust stroke or an expansion stroke, which injection is carried out after fuel from the injector 40 is injected to the combustion chambers 13 to be burned. Alternatively, unburned fuel may be added by adding fuel to the exhaust gas from the fuel addition valve 46 be supplied. In order to minimize extra fuel consumption due to the solids removal control, the amount of unburned fuel component added to the catalysts in the solids removal control is limited to the minimum required for a necessary increase in the temperature of the catalysts.

In this embodiment For example, the solid removal control is carried out when the following requirements all fulfilled are.

The removal of solids is required. A requirement for solids removal is made when clogging of the solids filter 26 based on the fact that the solid accumulation amount of the solid filter 26 , which is estimated by the engine operating state, reaches and exceeds the highest value of an allowable range.

A detected value of the input gas temperature sensor 28 (Input gas temperature thci) is greater than or equal to a lower limit temperature A (for example, 150 ° C) for carrying out the solids removal control. In addition, the catalyst bed temperature of the NOx catalyst, which is estimated from the progress of the engine operating condition, is greater than or equal to a lower limit temperature B for performing the solids removal control. The lower limit temperatures A, B are the lowest values of the exhaust gas temperature and the catalyst bed temperature, which cause sufficient oxidation to increase the catalyst bed temperature, in which an unburned fuel component is supplied.

The detected value of the input gas temperature sensor 28 is lower than an upper limit C in a temperature range for preventing excessive temperature increase of the catalysts due to heat generated by the solid removal control.

The detected value of the outlet gas temperature sensor 29 is lower than an upper limit D in a temperature range for preventing excessive temperature elevation of the catalysts due to the solids removal control.

Fuel addition to the exhaust gas is permitted. That is, the engine operating condition is in a range to allow the fuel addition to the exhaust gas. The addition of fuel to the exhaust gas in the internal combustion engine 10 is allowed as long as the machine 10 is not stalled, the cylinders have been differentiated, and the degree of depression of the accelerator pedal is not limited.

At the upstream end of the NOx catalyst 25 and the upstream end of the solids filter 26 some of the solids remain even when the above-described solids removal control is carried out. The reason why solids remain is believed to be due to solids at the exhaust top of the NOx catalyst 25 and the exhaust top end of the solids filter 26 and the supply of an unburned fuel component in the solids removal control may not provide a sufficient amount of unburned fuel component per unit time to completely burn the solids. Especially in the NOx catalyst 25 which is upstream of the solids filter 26 a larger amount of solids remains at the upstream end which is in the solids separator not be burned.

In this regard, a burn off control in the final stage of the solids removal control is performed to burn the solids that can not be burned in the solids removal control. The overview of the burn-off control will be explained with reference to FIG 2 (a) and 2 B) to be discribed. 2 (a) shows the way in which the fuel addition valve 46 Fuel admits, and 2 B) shows changes in the exhaust air-fuel ratio.

As in 2 (a) is shown, a concentrated, intermittent fuel addition in the burn-off control is repeatedly performed and stopped. The concentrated, intermittent fuel addition increases the amount of unburned fuel component and oxygen that are added to the catalysts of the NOx catalyst 25 and the solid filter 26 be supplied to a sufficient level for burning the solids that can not be burned in the solids removal control. Therefore, the concentrated, intermittent fuel addition allows the solids to be burned.

However, the concentrated, intermittent fuel addition causes the catalyst bed temperature to increase considerably. Therefore, in this embodiment, the fuel addition is periodically stopped to thereby suppress an excessive increase in the catalyst bed temperature. Consequently, an intermittent concentrated fuel addition is repeatedly performed and stopped, and the exhaust air-fuel ratio is repeatedly reversed between a rich state and a lean state, as in FIG 2 B) is shown. The burn-off control is terminated when the repetitions of performing and stopping the concentrated intermittent fuel addition has reached a number (three times in this embodiment) necessary to combust the solids present in the NOx catalyst 25 and the solid filter 26 remain, is sufficient.

The Solids removal control is based on the end of the burn off control stopped.

The procedure for the final stage defrosting control of the solids removal control will now be described with reference to FIG 3 describing a program or routine of the burn-off control. The burn-off control program is executed by the electronic control device 50 as an interruption, for example at predetermined time intervals.

In the program is determined (S101) whether the solids removal control currently performed becomes. If the solid removal control is performed, is determined (S102), whether a solid accumulation amount under one Determination value Since fallen. If the result of S102 is positive is, steps S103 to S105 for performing the burn-off control are performed.

The determination value Da is set to a value showing that in each of the NOx catalyst 25 and the solid filter 26 Solids in a section on a downstream side were completely burned by the solids removal control, and solids in a section on an upstream side were not completely burned by the solids removal control. For example, the determination value Da is set to 0.3 g. If the burn off control is performed with solids present in the downstream sections of the NOx catalyst 25 and the solid filter 26 remain and the solids are burned by the burn-off control, the temperature of these sections can be excessively increased. The value of the determination value Da is set to prevent such excessive increase of the sections.

The concentrated, intermittent fuel addition in the burn-off control serves no purpose except it is performed in a state in which the supplied fuel is evaporated and promotes burning of the solids. That's why in an operating state in which by the concentrated, intermittent Fuel added fuel is not evaporated, the Example in a low-load operating state in which the exhaust gas temperature not increased Preferably, the concentrated, intermittent fuel addition exposed.

Therefore is based on steps S103 to S105 for performing the burn-off control on, for example, the engine load and the engine speed (S103) determines whether the current operating state for performing the concentrated, intermittent fuel addition is suitable. The performing and stopping the concentrated, intermittent fuel addition is repeated only if the result of S103 is positive. If the result of step S103 is negative, the burn-off control occurs in a standby state (S105), and the concentrated, Intermittent fuel addition is not performed. however becomes even in the standby state of the burn-off control unburned fuel component contiguous to the catalysts supplied based on the solids removal control.

Step S106 and the following steps are for stopping the burn-off control and stopping the solids removal control based on the end of the burn-off control. In this order of steps, when the number of repetitions of performing and stopping the concentrated, intermittent fuel addition 3 is reached (positive result in S106), the burn-off control is ended (S108). Accordingly, the solids removal control is stopped (S109). However, if the burn-off control enters the standby state before the number of repetitions 3 reached and the standby state continues for a prolonged period, it is inevitable that the fuel consumption of the machine 10 is deteriorated by the amount of unburned fuel component supplied to the catalysts in the solids removal control.

Therefore in this embodiment, itself if the number of repetitions has not reached three (negative Result at S106), the burn-off control by the burn-off control ends (S108) when the elapsed time is a predetermined time t, since then, the amount of solid accumulation reaches a determination value Db is less than the determination value Da. If the elapsed time has reached the predetermined time t becomes based on, for example, a counter C determined. If the Solid accumulation amount brought to the predetermined value Db is, the counter starts C according to one other program away from 0 at each predetermined period of time. Based on the fact that the counter C has a determination value Reached Dc, which corresponds to the predetermined time t, the expired Time determines to have reached the predetermined time t. Then, based on the end of the burn-off control (S108), the solids removal control becomes stopped (S109). Therefore, a deterioration of the engine fuel economy becomes due to a prolonged Standby state of Abbrennsteuerung prevented.

In this embodiment the determination value Db is zero. The predetermined time t is set longer as a time to repeat the three consecutive times performing and stopping the concentrated, intermittent fuel addition the burn-off control is required, and sufficiently short about the deterioration of the fuel economy due to the execution of the solids removal control in the standby state, when an allowable level is exceeded to prevent. Since it usually takes 30 to 40 seconds to get one single cycle of a performing and stopping the concentrated, intermittent fuel addition can perform the predetermined time t is set to, for example, 180 seconds be.

Finally, the execution of the solids removal control and the burn-off control will be described with reference to the timing charts of FIGS 4 (a) to 4 (b) to be discribed. 4 (a) to 4 (b) FIG. 15 are timing charts showing changes in the amount of solid accumulation, the state of the solid removal control, the state of the burn-off control, and changes of the counter C, respectively.

At a time T1, the solids removal control is started. Then, the solid accumulation amount has been reduced and dropped below the determination value Da at a time T2 at which the burn-off control is started. During the burn-off control, if the burn-out control standby state continues for an extended period of time, the end of the control is delayed as indicated by a two-dot chain line in FIG 4 (c) is shown. Accordingly, the end of the solids removal control is delayed based on the flow rate of the burn-off control as indicated by a two-dot chain line in FIG 4 (b) is shown. Consequently, the fuel economy will degrade by the amount of unburned fuel component supplied to the catalysts based on the solids removal control in the standby state.

However, in this embodiment, when the elapsed time reaches the predetermined time t, since the solid accumulation amount has been zeroed by the burn-off control (the determination value Db), that is, when the counter C reaches the determination value Dc (time T4), the burn-off control forcibly ended, as indicated by a solid line in 4 (c) is shown. In accordance with the forcible end of the burn-off control, the solids removal control is stopped as indicated by the solid line in FIG 4 (b) is shown. This suppresses the deterioration of engine fuel economy.

• (1) Feststoffe in stromaufwärtigen Abschnitten des NOx-Katalysators 25 und des Feststofffilters 26, die durch die Feststoffentfernungssteuerung nicht gänzlich verbrannt werden können, werden durch die Abbrennsteuerung gänzlich verbrannt, die in der Endphase der Feststoffentfernungssteuerung durchgeführt wird. Deshalb, wenn das Abgas-Luft-Kraftstoff-Verhältnis nach dem Ende der Feststoffentfernungssteuerung fetter gemacht wird, werden keine an den stromaufwärtigen Enden des NOx-Katalysators 25 und des Feststofffilters 26 verbleibenden Feststoffe verbrannt, so dass die Temperatur der Katalysatoren an einem übermäßigen Ansteigen gehindert wird.
• (2) Wenn der Bereitschaftszustand der Abbrennsteuerung für einen ausgedehnten Zeitraum andauert, wird die Abbrennsteuerung zwangsweise unter der Bedingung angehalten, dass die abgelaufene Zeit, seitdem die Feststoffansammlungsmenge durch die Abbrennsteuerung auf dem Bestimmungswert Db (0) gebracht ist, die vorbestimmte Zeit t erreicht. Deshalb, selbst wenn der Bereitschaftszustand der Abbrennsteuerung über einen ausgedehnten Zeitraum anhält, wird die Kraftstoffökonomie der Maschine nicht verschlechtert werden.
• (3) Die vorbestimmte Zeit t ist länger eingestellt als die Zeit, die zum dreimaligen nacheinander Ausführen des Durchführen und des Anhaltens der konzentrierten, intermittierenden Kraftstoffzugabe der Abbrennsteuerung erforderlich ist, und ausreichend kurz ist, um die Verschlechterung der Kraftstoffökonomie aufgrund der Durchführung der Feststoffentfernungssteuerung durch den Bereitschaftszustand an einem Übersteigen eines zulässigen Niveaus zu hindern. Deshalb, falls von dem Bereitschaftszustand der Abbrennsteuerung erwartet wird, derart ausgedehnt zu werden, dass eine Verschlechterung der Kraftstoffökonomie unzulässig wird, wird die Abbrennsteuerung zwangsweise beendet. Entsprechend wird die Kraftstoffökonomieverschlechterung auf ein zulässiges Niveau gedrückt.
• (4) Da sich der NOx-Katalysator 25 stromaufwärts von dem Feststofffilter 26 in dem Abgasdurchgang 14 befindet, sammeln sich Feststoffe wahrscheinlich an dem stromaufwärtigen Ende des NOx-Katalysators 25. Entsprechend wird die Menge an Feststoffen, die durch die Feststoffentfernungssteuerung nicht gänzlich verbrannt werden können, erhöht. In den Abschnitten, in denen Feststoffe nicht gänzlich verbrannt werden, ist der Oberflächenbereich der Katalysatoren, die dem Abgas ausgesetzt sind, reduziert. Dies verzögert die Aktivierung der Katalysatoren. Entsprechend wird die Wärme reduziert, die während der Abgasreinigung in den Katalysatoren erzeugt wird. Folglich wird die Wärme reduziert, die von dem NOx-Katalysator 25 zu dem stromabwärts befindlichen Feststofffilter 26 übertragen wird. Dies behindert die Aktivierung des Katalysators in dem Feststofffilter 26. Folglich kann das Abgasreinigungsverhalten herabgesetzt werden. Jedoch werden diese Nachteile durch ein gänzliches Verbrennen von Feststoffen beseitigt, die an dem stromaufwärtigen Ende des NOx-Katalysators 25 verbleiben, durch die Abbrennsteuerung in der Endphase der Feststoffentfernungssteuerung.

The above-described embodiment has the following advantages.

• (1) Solids in upstream sections of the NOx catalyst 25 and the solid filter 26 which can not be completely burned by the solids removal control are completely burned by the burn-off control performed in the final stage of the solids removal control. Therefore, when the exhaust air-fuel ratio is made richer after the end of the solid-removal control, none at the upstream ends of the NOx catalyst 25 and the solid filter 26 remaining solids burned, so that the temperature of the catalysts is prevented from excessive increase.
• (2) When the standby state of burning off If the control continues for an extended period of time, the burn-off control is forcibly stopped under the condition that the elapsed time since the solid accumulation amount is brought to the determination value Db (0) by the burn-off control reaches the predetermined time t. Therefore, even if the standby state of the burn-off control continues for an extended period of time, the fuel economy of the engine will not be degraded.
• (3) The predetermined time t is set longer than the time required for executing the lumping control intermittent fuel addition and stopping three times in succession, and is sufficiently short to allow the deterioration of the fuel economy due to the solid removal control to be performed to prevent the standby state from exceeding an allowable level. Therefore, if it is expected from the standby state of the burn-off control to be extended so that deterioration of the fuel economy becomes inadmissible, the burn-off control is forcibly terminated. Accordingly, the fuel economy deterioration is suppressed to a permissible level.
• (4) Since the NOx catalyst 25 upstream of the solids filter 26 in the exhaust passage 14 As a result, solids are likely to accumulate at the upstream end of the NOx catalyst 25 , Accordingly, the amount of solids that can not be completely burned by the solids removal control is increased. In sections where solids are not completely burned, the surface area of the catalysts exposed to the exhaust gas is reduced. This delays the activation of the catalysts. Accordingly, the heat generated during exhaust gas purification in the catalysts is reduced. Consequently, the heat generated by the NOx catalyst is reduced 25 to the downstream solids filter 26 is transmitted. This hinders the activation of the catalyst in the solids filter 26 , Consequently, the exhaust gas purification performance can be reduced. However, these disadvantages are eliminated by a total burning of solids at the upstream end of the NOx catalyst 25 remain, by the Abbrennsteuerung in the final phase of the solids removal control.

The previously described embodiments can be modified as follows.

The order of the NOx catalyst 25 , the solid filter 26 and the oxidation catalyst 27 along the exhaust passage 14 can be changed as required.

In the burn-off control, the number of repetitions of performing and stopping the concentrated intermittent fuel addition is not limited to three as long as the number of remaining solids in the NOx catalyst completely burns 25 and the solid filter 26 is sufficient.

The determination value Da is not limited to 0.3 g, which is shown in the above-described embodiment, as long as the value Da shows that solids at the downstream portions of the NOx catalyst 25 and the solid filter 26 were completely burned.

Of the Determination value Db does not have to be 0, but can be on any Value changed which is lower than the determination value Da.

The present examples and embodiments should be considered as illustrative and not restrictive, and the invention is not limited to the details given herein, but may be modified within the scope of the appended claims become.

Claims (4)

Exhaust gas purification device for an internal combustion engine ( 10 ), wherein the apparatus performs a solids removal control, in which an unburned fuel component is supplied to a catalyst, which is in an exhaust system of the internal combustion engine ( 10 ), so that the temperature of the catalyst is increased and the solids stuck to the catalyst are burned, the apparatus is characterized by: an embodiment in which, when an accumulation amount of particulates on the catalyst becomes smaller than a first determination value (Da), after the solids removal control is started, the execution means executes a burn-off control in which a performing and stopping of a concentrated intermittent fuel addition to a portion of the exhaust system upstream of the catalyst is repeated at a predetermined frequency; a stopper that stops the solids removal control based on an end of the burn-off control; and compulsory completion means that forcibly terminates the burn-off control when, after the start of the burn-off control, an elapsed time since the accumulation amount of particulates on the catalyst has fallen to a second determination value (Db) reaches a predetermined time (t), the second determination value (Db) is less than the first determination value (Da). device according to claim 1, characterized in that the predetermined time (t) longer as is a time required to carry out and Stopping the concentrated, intermittent fuel addition continuously repeat the burn-off control at the predetermined frequency, and is sufficiently short to worsen fuel economy due to the implementation solid removal control in the predetermined time (t) to prevent. Apparatus according to claim 1 or 2, characterized in that the catalyst through a solid filter ( 26 ) and a NOx catalyst ( 25 ), which are placed one behind the other in the exhaust system. Exhaust gas purification method for an internal combustion engine ( 10 ), the method is characterized by: performing a solids removal control in which an unburned fuel component is supplied to a catalyst which is in an exhaust system of the internal combustion engine ( 10 ), so that the temperature of the catalyst is raised and solids stuck to the catalyst are burned; Performing a burn-off control when an accumulation amount of particulates on the catalyst becomes smaller than a first determination value (Da) after the solids removal control is started, wherein in the burn-off control, performing and stopping a concentrated intermittent fuel supply to a portion of the exhaust system upstream from the catalyst is repeated at a predetermined frequency; Stopping the solids removal control under the condition that the burn-off control is ended; and forcibly terminating the burn-off control when, after the start of the burn-off control, an elapsed time since the accumulation amount of particulates on the catalyst has been reduced to a second determination value (Db) reaches a predetermined time (t), the second determination value (Db) being less than the first determination value (Da) is.